The present invention relates to an apparatus for reducing intraocular pressure. In particular, the present invention is directed to an apparatus configured for implantation in the eye for the purpose of draining aqueous from the anterior chamber of the eye, thereby reducing intraocular pressure. Glaucoma is a disease marked by an increase in intraocular pressure. The increase in intraocular pressure is principally attributable to a failure of the tissues of the eye to drain aqueous from the anterior chamber of the eye at an adequate rate, although in certain cases an over-production of aqueous by the eye is the cause of the increased pressure. Over time, persistently heightened intraocular pressure will cause permanent damage to ocular tissues, often resulting in blindness. For this reason, it is desirable to maintain the intraocular pressure at It physiologically acceptable level.
Various techniques have been used in an effort to control intraocular pressure. For example, hypotensive agents are commonly prescribed in an effort to reduce the production of aqueous by the eye. Although the use of such hypotensive agents is effective in some cases, this pharmacological approach fails to address the true cause of the increased intraocular pressure, i.e., the failure of the eye to drain aqueous from the anterior chamber. Thus, in many patients it becomes necessary and desirable to facilitate the drainage of aqueous from the anterior chamber of the eye through the use of an implantable drain or shunt.
A variety of devices have been-proposed and used by various ophthalmologists for the purpose of draining aqueous from the anterior chamber of the eye. For example, U.S. Pat. No. 4,457,757 to Molteno discloses a shunt that includes a tube fluidly connected at its first end to a plate. The second end of the tube is configured for insertion into the anterior chamber of the eye, thereby providing a flow path from the anterior chamber to the plate. The plate portion of the Molteno device is configured to lie on the external surface of the eye following implantation of the second end portion of the tube in the anterior chamber. Shunt devices of the type disclosed by Molteno commonly produce an undesirable drop in intraocular pressure, i.e., hypotonicity, immediately following implantation, thereby resulting in damage to the ocular tissues. In addition, such devices provide no ability to control the flow rate of aqueous therethrough. Thus, these implants cannot be adjusted to suit the needs of the particular person into which they are implanted. Accordingly, it is desirable to provide a shunt device that is capable of providing a flow path for the removal of aqueous from the anterior chamber of the eye without causing hypotonicity. In addition, it is desirable to provide a shunt device whose flow resistance can be adjusted so as to accommodate the needs of the particular patient into which it is implanted.